Recently, photographic silver halide emulsions have been required having improved photographic properties including high sensitivity, high contrast and excellent graininess.
It is known that for attaining good photographic properties such as high sensitivity, high contrast and excellent graininess, mono-dispersed silver halide emulsions having a narrow grain size distribution as described in, for example, U.S. Pat. No. 4,184,877 corresponding to Japanese Patent Application (OPI) No. 153428/77 are advantageous (The term "OPI" as used herein refers to a "published unexamined Japanese patent application"). It is also useful to increase the utilization efficiency of incident light by using core/shell type silver halide emulsion grains having a silver halide phase of a different composition in the inside of the emulsion grain so that the functions involved in the procedure of from the receipt of light to the image formation can be shared by the core portion and the shell portion of the emulsion grain as completely as possible such that the core portion can catch positive holes to prevent them from combining with photoelectrons, thereby inhibiting the development and preventing the deterioration of graininess, while the shell portion can concentrate photoelectrons therein and form latent images (silver nuclei) efficiently, as described in, for example, Research Disclosure 163 p.45-46 (November 1977), J. Photo. Sci. 26 p.189 (1978), U.S. Pat. Nos. 3,317,322, 3,850,637 and 3,206,313, Research Disclosure 108 p.4 (April 1973) and ibid. 113 p.57 (September 1973), and Phot. Sci. & Eng. 19 p.344(1975).
Furthermore, in order to obtain silver halide emulsions of high contrast it is preferred to narrow the distribution of the silver halide composition between silver grains.
In order to evaluate the distribution of the halogen composition of silver halide grains, the known powder X-ray diffraction method described in, for example, U.S. Pat. No. 4,349,622 corresponding to Japanese Patent Application (OPI) NO. 110926/81 can be used. However, since the method is insufficient in resolving power, it is difficult to evaluate the distribution of the halogen composition between silver halide grains. Also, since the distribution of the halogen composition between individual silver halide grains cannot be distinguished from the general distribution of the halogen composition in the silver halide grains using this method, it is impossible to evaluate the distribution of the halogen composition between silver halide grains having the particular distribution of halogen composition required in the core/shell type silver halide emulsions for use in this invention. Therefore, although silver halide emulsions having a controlled distribution of halogen composition in the inside of silver halide grains by mono-dispersing the grain size distribution of the grains in the emulsion have widely been investigated, it is actually impossible to prepare silver halide emulsions meeting such practical requirements of narrow distribution of the halogen composition between silver halide grains. Practical methods of preparing such silver halide emulsions have not yet been disclosed.
The inventors have measured the halogen composition of individual grains of a silver iodobromide emulsion using an X-ray microanalizer and have established that there is a large discrepancy in the halogen composition of individual silver halide grains, which reduces the photographic properties.